Recently, there are more researches on electronic control of construction machines for intelligent excavation. In particular, an electronic proportional pressure reducing valve (EPPRV) is applied to a main control valve to electronically control the construction machine.
The electronic proportional pressure reducing valve may control, with an electrical signal, a motion of a spool for controlling a supply of a main working fluid to a traveling device and various types of working devices that require hydraulic pressure. For example, a main control valve to which the electronic proportional pressure reducing valve is applied may adjust a position of the spool in proportion to a voltage signal or a current signal applied to the electronic proportional pressure reducing valve. Specifically, the main control valve may include multiple spools, and multiple electronic proportional pressure reducing valves which are connected to the multiple spools, respectively. Further, the multiple electronic proportional pressure reducing valves adjust a pilot working fluid applied to the multiple spools to control motions of the multiple spools.
However, in a case in which there is something wrong with any one of the multiple electronic proportional pressure reducing valves or with a control unit for controlling the multiple electronic proportional pressure reducing valves, the spool moves even though an operator does not manipulate a manipulating device, and for this reason, the construction machine operates, which causes a safety accident. Accordingly, there is a need for a solution for preventing the safety accident.